It may involve choosing a word that fits in with the grammar of the sentence. For example:
He never ... in reaching the source of the river
a. managed b. achieved c. arranged d. succeeded
The only answer is “succeeded”, not because it is the only word that fits in with the meaning but because it’s the only one that is followed by “in” and a gerund.
It can test “fixed phrases”
It may involve choosing a word that fits in a set phrase. For example:
They didn’t ... notice of me, so I left.
a. pay b. take c. get d. bring
The answer is “take” because it is part of the phrase “take notice of”.
It can test “phrasal verbs”
It may involve choosing a word that forms a phrasal verb, with the correct meaning. For example
Scientists have been quick to ... out the problems with the new theory.
a. give b. point c. let d. come
The answer is “point”, not because the other words do not form phrasal verbs with the word “out”, but because “point out” fits in with the meaning of the sentences.